With one suspect dead and the other captured and lying grievously wounded in a hospital, the investigation into the Boston Marathon bombings turned Saturday to questions about the men’s motives, and to the significance of an overseas trip one of them took last year.

Federal investigators are hurrying to review a visit that one of the suspected bombers made to Chechnya and Dagestan, predominantly Muslim republics in the north Caucasus region of Russia. Both have active militant separatist movements. There are concerns in Congress about the FBI’s handling of a request from Russia before the trip to examine the man’s possible links to extremist groups in the region.

Dzhokhar Tsarnaev. Photo: Reuters

Tamerlan Tsarnaev, who died early Friday after a shootout with police in Watertown, Massachusetts, spent six months of last year in Dagestan.

Advertisement

Tamerlan’s father, Anzor, said his son had returned to renew his passport, but his stay was prolonged and, analysts said, may have marked a crucial step in his path toward the bombing of the Boston Marathon.

Kevin R. Brock, a former senior FBI and counterterrorism official, said, ‘‘It’s a key thread for investigators and the intelligence community to pull on.’’

Tamerlan Tsarnaev. Photo: Reuters

The investigators began scrutinising the events in the months and years before the fatal attack, as Boston began to feel like itself for the first time in nearly a week.

Monday had brought the bombing, near the finish line of the Boston Marathon, which killed three and wounded scores, and the tense days that followed culminated in Friday’s lockdown of the entire region as police searched for Tsarnaev’s younger brother from suburban backyards to an Amtrak train bound for New York City.

The motivations of Tamerlan Tsarnaev, and his younger brother, Dzhokhar, who was taken into custody Friday night and is still too injured to speak, are as yet publicly unknown. Of Chechen heritage, they lived in the United States for years, according to friends and relatives, and no direct ties have been publicly established with known Chechen terrorist or separatist groups.

The significance of the trip was magnified late Friday when the FBI disclosed in a statement that in 2011 ‘‘a foreign government’’ — now acknowledged by officials to be Russia — asked for information about Tamerlan, ‘‘based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country’s region to join unspecified underground groups.’’

The senior law enforcement official said the Russians feared he could be a risk, and ‘‘they had something on him and were concerned about him, and him traveling to their region.’’

But the FBI never followed up on Tamerlan Tsarnaev once he returned, a senior law enforcement acknowledged on Saturday, adding that the bureau had not kept tabs on him until he was identified on Friday as the first suspect in the marathon bombing case.

President Barack Obama and Republican lawmakers devoted their weekly broadcast addresses to the Boston attack, with both sides finding a common voice.

Russia and the United States have since 1994 routinely exchanged requests for background information on residents traveling to each other’s countries on visa, criminal or terrorism issues. It was unclear Saturday whether Russia makes requests of any American traveler of Chechen origin to Russia, or if the Russian government offered the FBI specific evidence in the case of Tamerlan Tsarnaev.

The bureau responded to the request by checking ‘‘U.S. government databases and other information to look for such things as derogatory telephone communications, possible use of online sites associated with the promotion of radical activity, associations with other persons of interest, travel history and plans, and education history,’’ the statement explained.

In January 2011, two agents from the bureau’s Boston field office interviewed Tamerlan and family members, a senior law enforcement official said on Saturday. According to the FBI’s statement, ‘‘The FBI did not find any terrorism activity, domestic or foreign,’’ and conveyed those findings to ‘‘the foreign government’’ by the summer of 2011.

As the law enforcement official put it, ‘‘We didn’t find anything on him that was derogatory.’’

The Russian state news agency RIA Novosti quoted the father of the Tsarnaev brothers recalling the FBI’s close questioning of his elder son, ‘‘two or three times.’’

He said they had told his son that the questioning ‘‘is prophylactic, so that no one sets off bombs on the streets of Boston, so that our children could peacefully go to school.’’

In an interview in Russia, Zubeidat Tsarnaeva, the mother of the two men, recalled that the agents had told her that Tamerlan was ‘‘an excellent boy,’’ but ‘‘at the same time, they told me he is getting information from really extremist sites, and they are afraid of him.’’

After the visit to Dagestan and Chechnya, signs of alienation emerged. One month after Tamerlan returned to the United States, a YouTube page that appeared to belong to him was created and featured multiple jihadi videos that he had endorsed in the past six months.

One video features the preaching of Abdul al-Hamid al-Juhani, an important ideologue in Chechnya; another focuses on Feiz Mohammad, an extremist Salafi Lebanese preacher based in Australia. He also created a playlist of songs by a Russian musical artist, Timur Mucuraev, one of which promotes jihad, according to the SITE Intelligence Group, which monitors statements by jihadists.

The aftermath of the arrests has thrust Washington and Moscow into a cooperative mode, a jarring shift coming amid weeks of rancor over American criticism of Russia’s human rights record. Obama and Russian President Vladimir V. Putin spoke by telephone late Friday night, in a conversation initiated by the Russian side, the Kremlin announced. The Kremlin’s statement said both leaders expressed ‘‘the building of close coordination between Russian and American intelligence services in the battle with global terrorism.’’

Nevertheless, there were glaring questions about the case, among them how Tamerlan had escaped attention after 2011.

A Russian intelligence official told the Interfax news service on Saturday that Russia had not been able to provide the United States with ‘‘operatively significant’’ information about the Tsarnaev brothers, ‘‘because the Tsarnaev brothers had not been living in Russia.’’

Andrei Soldatov, an investigative journalist who specialises in Russia’s security services, said he believes that Tamerlan may have attracted the attention of Russian intelligence because of the video clips he had posted under his own name starting in 2010, which were included on a list of banned materials by the Federal Security Service, or FSB.

At that point, the agency had just begun routinely scrutinising materials posted on social networks, and would most likely have sent a request to the FBI, said Soldatov, the author of The New Nobility: The Restoration of Russia’s Security State and the Enduring Legacy of the KGB.

On Saturday morning, federal prosecutors were drafting a criminal complaint against Dzhokhar A. Tsarnaev, 19, who was wounded in the leg and neck and had lost a great deal of blood when he was captured Friday evening. The FBI and local law enforcement agencies continued to gather evidence and investigate the bombings, the slaying of a Massachusetts Institute of Technology police officer Thursday night and the subsequent battle with the police that left another officer critically wounded.

An official said the criminal complaint would likely include a constellation of charges stemming from both the bombings and the shooting, possibly including the use of weapons of mass destruction, an applicable charge for the detonation of a bomb. That charge, the official said, carries a maximum penalty of death. While Massachusetts has outlawed the death penalty, federal law allows it.

Muslim leaders in many cities rushed to hold news conferences and preach sermons at mosques denouncing the bombing suspects, mourning the victims and praising the response of law enforcement and the community in Boston. They were eager to disassociate their faith from the Muslim suspects, and to head off a backlash against Muslims in the United States.

Anzor Tsarnaev and his younger son first came to the United States legally in April 2002 on 90-day tourist visas, federal law enforcement officials said. Once in this country, the father applied for political asylum, claiming he feared deadly persecution based on his ties to Chechnya. Dzhokhar, who was 8, applied for asylum under his father’s petition, the officials said, and became a naturalised citizen on September 11 last year. Tamerlan Tsarnaev came to the United States later, and applied for American citizenship on September 5 last year, federal law enforcement officials said.

Although Anzor Tsarnaev has said his older son’s citizenship application had been denied — and certainly would have been if he were under suspicion as a potential terrorist — the officials said it was still in process and had not been either approved or denied.

As a routine part of his application, Tamerlan Tsarnaev was subject to a criminal-background check by the FBI. The authorities confirmed that he had been involved in a domestic violence incident while he was a resident with a green card, the officials said. A review of the episode delayed his citizenship application, the officials said, but it was not deemed serious enough to disqualify his application.

21 Apr
As their photographs spread rapidly across the internet, the Tsarnaev brothers decided to move. Not waiting for police to find them, they gathered guns and homemade explosives for what became a final, bloody rampage on a community still in shock from the bombings three days before.

21 Apr
A spotlight is thrown on one of the darkest corners of nationalist and Islamic militancy, to a campaign for separatism and vengeance responsible for some of the most unsparing terrorist acts of recent decades.

22 Apr
With one suspect dead and the other captured and lying grievously wounded in a hospital, the investigation into the Boston Marathon bombings turned to questions about the motives, and to the significance of an overseas trip one of them took last year.